1. Field of the Invention
This invention relates to photographic apparatus and, more particularly, to a motion picture rear projection viewing screen.
2. Description of the Prior Art
A rear projection viewer apparatus in which the projection system and the viewing screen are combined in a single structural unit are well known in the prior art. Among other advantages, this type of projector apparatus can provide a compact portable unit which permits satisfactory pictorial displays in high ambient light conditions, and is particularly suited to those instances where available space is limited. Conventionally, apparatus of this type employ a lenticular screen arrangement which directs the projected images over a controlled viewing zone centered along an axis normal to the screen, and hence, do not generally provide a suitable arrangement for directing the viewing zone to an audience located off the screen axis.
In apparatus of this type where a compact system is employed, wide angle projection is commonly utilized, and hence, the viewing screen must also provide a collimating function. An arrangement commonly used in such viewing apparatus is a compound screen structure making use of a Fresnel lens to collimate the transmitted image and a lenticular screen arrangement utilizing a plurality of contoured lenticules for controlled uniform dispersion of the transmitted image over a given viewing zone. A typical screen of this design is shown and described in U.S. Pat. No. 3,848,980 entitled "Projector Apparatus and System Employing Unique Screen" issued Nov. 19, 1974. One of the drawbacks of such a screen design has been the necessity of limiting the horizontal and vertical viewing angles to a relatively small angle in order to provide a sufficiently bright image under ambient light conditions within that viewing region. Recent improvements have resulted in an increase in the brightness of the viewable image within the angular viewing zone. As a result, changes in the contour of the lenticular elements have been experimented with in order to increase the viewing region. It has been found, however, that as the contour of the lenticular elements, i.e., specifically the steepness of the sides of the lenticules has been changed in order to increase the viewing angle, the intensity of back brightness or total internal reflection from these lenticules has increased dramatically. Accordingly, the available viewing angle has been severely limited by the necessity of keeping the back brightness to a tolerable level to permit a good viewable image under normal ambient lighting conditions.